> No, chain-of-trust only has one trick... it can check that what you're about to run is unaltered from what was signed to some degree of probability.
This is only one of many privacy and security regressions from moving to a far less secure software stack without anything close to the same level of hardening or work on privacy / security.
> If that is the - shipped and validly signed - bugridden nightmare-fuel like the propreitary Qualcomm 802.11 stack or proprietary multimedia bits that are a rich and continuous source of vulnerabilities (take a look through the last months here https://source.android.com/security/bulletin/2019-06-01 ) all the buzzwords did was ensure the vulnerable version is running so it can be exploited. The evil maid can get in that way.
Counting CVEs is not a way to judge security. Qualcomm's SoC hardware, firmware and driver security is the leader among the available options. The huge amount of both internal and external public security research targeting it is a strength rather than a weakness. The lack of attention given to other assorted drivers is not a strength of those drivers but rather reflects their obscurity and lack of hardening / auditing.
It's also not the norm in the Linux world to assign a CVE for a security vulnerability when it's fixed. The norm is to fix them silently without trying to obtain a CVE. It's completely bogus to judge security based on counting CVEs for many reasons. Not having public lists of the fixed vulnerabilities with CVEs assigned doesn't mean there aren't a bunch of vulnerabilities being fixed, and it's even worse if the vulnerabilities aren't being found and fixed.
Every x86 and ARM device is proprietary and has a massive amount of complex proprietary hardware, firmware and microcode. There is no escaping that for these architectures. The Librem 5 is not an open hardware device and has a proprietary SoC, proprietary Wi-Fi, etc. all with their own proprietary firmware and in some cases entire operating systems (Wi-Fi / Bluetooth, cellular, etc.). The distinction of an OS like PureOS is that they don't ship updates to this firmware but rather leave it vulnerable to all the fixed security issues, because they won't redistribute the proprietary firmware updates. The firmware is still present, but the OS is 'free'. Either way, that firmware is running, and with a bunch of known vulnerabilities if you don't update it.
Proprietary hardware and software is also not inherently less private or secure than open source software. These are differences in development model, not privacy or security. You're very mistaken if you think open source software eliminates backdoors / vulnerabilities or even reduces them. It's not how things work out in reality. Open source reduces the barrier to entry for security research, whether it's for good or evil, but it's certainly still possible without it being open source. Either way, the comparison you're making is between proprietary hardware + proprietary firmware + open source OS to proprietary hardware + proprietary firmware (but without updates shipped by the OS) + open source OS.
> Librem's security model is that of a Linux box, signed update packages
Again, you're mixing hardware and software. The Librem hardware isn't only for PureOS and will be able to run Android.
Signed update packages alone are inferior to not only having signed update packages but also verified boot and attestation. GPG also has far too much complexity and attack surface for this, and having online build / signing servers, etc. is a joke.
Android is Linux, and the Linux kernel is not a strength but rather the most prominent weakness in Android. A massive monolithic kernel written entirely in a memory unsafe language and entirely responsible for enforcing the low-level privacy/security model is not a strength. That's a major problem which needs to be resolved, not a hole to dig deeper. It's fundamentally not fixable and while a bunch of work on mitigations can help, it's very limited in what can be achieved. Moving to the desktop Linux software stacks also gives up the vast majority of these mitigations and the security model that has been rapidly improved over the years. It gives up having such strict SELinux policies developed as an integral part of the base system, as just one of many things that are lost. This level of security cannot be obtained on a traditional Linux distribution without a well-defined base system that's developed together with lots of holistic systems level privacy and security work. Addressing it in a bunch of separate fragmented projects doesn't work out, and prevents having the same kind of security model and security policies. The way that SELinux is used on Android compared to a distribution like RHEL / Fedora is day and night. It's drastically different and not even comparable at all. The same goes for the deployment of other privacy and security features / models.